The Type 755 actuator is a pneumatically operated, spring opposed diaphragm actuator designed specifically to fit the Research Control Valve body-bonnet assembly.

Description

The Type 755 actuator is a pneumatically operated, spring opposed diaphragm actuator designed specifically to fit the Research Control Valve body-bonnet assembly. The unit is available in two sizes: one to fit the 1/4 in. (6 mm) valve and a larger version to fit the 1/2…1 in. (12…25 mm) valves. It provides smooth linear extension of the valve stem upon an increasing instrument signal. A decrease in instrument signal causes the stem to retract and open the valve.

Downward closing force is generated by instrument air on top of the diaphragm. An increasing pressure in the diaphragm cavity opposes the force of the spring and extends the stem, closing the valve. The unit is designed to retract the stem, opening the valve, should the instrument signal fail.

FUNCTION

The 1/4 in. (6 mm) size 755 actuator normally operates in response to a 3…15 psi (0.2…1 bar) change in instrument signal, or a 12 psi (0.8 bar) range. This signal range causes the valve to stroke a distance of approximately 7/16 in. (11 mm). The standard spring has a deflection rate of 25 pounds per 1/8 in. (3 mm) and operates against an effective diaphragm area of approximately 7 in.2 (4516 mm2).

The 1/2 in. (12 mm) size 755 actuator also normally operates in response to a 3…15 psi change in instrument signal, or a 12 psi (0.8 bar) range. This signal range causes the valve to stroke a distance of approximately 9/16 in. (14 mm). The standard spring in the 1/2 in. (12 mm) unit has a deflection rate of 30 pounds per 1/8 in. (3 mm) and operates against an effective diaphragm area of approximately 11 in.2 (7096 mm2).

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